Vibration analyzer



April 9, 1968 P. K. TRIMBLE ET AL 3,376,733

VIBRATION ANALYZER Original Filed May 29, 1961 6 SheetS-Sheet IN V ENTORS April 9, 1968 P. K. TRxMBLE ET AL 3,376,733

VIBRATION ANALYZER Original Filed May 29, 15561 6 Sheets-Sheet, 3

VIBRATION ANALYZER Original Filed May 29, 1961 5 Sheets-Sheet L ATTORNEYApril 9, 1968 P. K.TR1MB1 E ET AL VIBRATION ANALYZER Original Filed May29, 1961 6 Sheets-Sheet 5.-,

April 9, 1968 P. K. TRI'MBLE ET Al- VIBRATION ANALYZER Original FiledMay 29, 1961 6 Sheets-Sheet G ATTURNEY UmeaV states Patent o r 3,376,733VEBRATION ANALYZER Philip K. Trimble, Rochester, and Edgar D. Walton,De-

troit, Mich., assignors to General Motors Corporation, Detroit, Mich., acorporation of Delaware Continuation of application Ser. No. 113,341,May 29, 1961. This application May 12, 1966, Ser. No. 549,732 19 Claims.(Cl. 7371.4)

ABSTRACT OF THE DISCLOSURE A vibration analyzer for isolating andevaluating the vibrations from various individual components of arotating assembly, such as an internal combustion engine having severalaccessories, each driven at a speed different from engine speed. Onepickup senses the vibrations of the assembly and develops a complexwave-shaped signal having the frequency components to be analyzed.Another pickup develops a reference signal of the same frequency as thespeed of the assembly. A portion of the reference signal, selectedaccording to the relation of the speed of the component to the assemblyspeed, drives a variable frequency oscillator. This variable frequencyoscillator develops a square wave-shaped output of a frequencyapproximate that of the selected component and is mixed by synchronousrectification with the complex signal for filtering purposes. Theresultant synchronously rectified signal is fed back to the oscillatorto alter the phase and the frequency thereof so that the oscillator willlock-in on the frequency of the selected component, at which time thesquare wave output from the oscillator and the complex signal will be 90out of phase and the synchronously rectified signal will be nulled. Theoscillator output is also phase shifted 90 to again synchronouslyrectify the complex signal and develop therefrom an output that isutilized for amplitude and frequency readout purposes.

This is a continuation of application Ser. No. 113,341, filed May 29,1961, now abandoned.

This invention relates to frequency analyzers and more particularly tovibration analyzers capable of determining the amplitude and frequencyof various frequency components of complex vibration signals.

In order to analyze complex vibrations produced by rotating parts,especially assemblies of connected accessories I 3,376,733 Patented Apr.9, 1968 still other speeds. For example in a typical installation thefan may run at 0.9 times crankshaft speed. In the case of an engineoperating at 1200 r.p.m. or 20 cycles per second, the fan will operateat 1080 r.p.m. or 18 cycles per second. Since the vibrations caused bythe crankshaft and fan operating at these speeds are only two cyclesapart, conventional filters do not have the selectivity to effectivelyseparate such vibrations.

An additional problem may exist in analyzing complex vibrations sincethe vibrations of various parts may be objectionable only at certainspeeds. A practical usable vibration analyzer must therefore be capableof tracking or analyzing the various vibration components throughout thefull speed range of the engine and associated members. Narrow band passfilters designed to pass only a single narrow frequency band generallycannot function throughout the wide range necessary to analyze thevibrations in an installation such as an automotive or aircraft engine.While it has been suggested to use heterodyne analyzers usingintermediate frequency filters, these have limitations both as to theminimum bandwidth that can be effectively filtered and as to the minimumfrequency that can be effectively filtered. Heterodyne filters usuallyrequire mechanical tuning arrangements, such as variable capacitors,that require expensive and heavy servo motors to tune the same forautomatic tracking control. Furthermore, heterodyne filters usuallyrequire expert calibration and use in order to effectively use theanalyzer to analyze two frequencies quite close together, for examplewithin two cycles of each other.

One method of providing highly selective filtering of complex waveformsproduced by transducers connected to rotating members has been developedusing synchronous controlled rectifiers such as mechanical choppers oreven more effectively by synchronous controlled rectifier bridges. Bysynchronizing the rectifiers to the rotation of the part being checked,the synchronous rectifier can be used to measure only the vibrationsoccurring at the same frequency as the rotational frequency of the partwhose vibrations are being analyzed. An example of the use of suchfilters is shown in U.S. Patent 2,787,907 in the name of William F. Kingand entitled Crankshaft Balancing Machine.

It would be desirable to further this type ofanalysis by being able tosynchronize the controlled rectifier filters with the rotation of partsand accessories other than the main rotating part without having toprovide separate synchronizing or reference signal connections to theseparts. It would furthermore be desirable to be able toprovide avibration analyzer that would be able to selectively indicate both themagnitude and frequency of vibration of the various rotating members ofa group of connected parts, as an engine and its accessories, merely byswitching a selector switch from one position to another.

It is therefore an object of this invention to provide a vibrationanalyzer that will effectively measure the magnitude of vibration, bothrelative and absolute, as well as the frequency of a plurality ofrotating members operating at various and different speeds and togetherproducing a complex vibration.

It is a further object to provide such an analyzer that willautomatically track these vibrations as their frequencies changethroughout a relatively large range.

It is still a further object to provide an analyzer wherein a singlevibration pickup and signal reference or syn chronizing pickup can beattached at a single point to a complex machine having a plurality ofrotating parts op erating at varying and different speeds and capable ofindependently and selectively measuring the vibrations caused byunbalance in each part.

Still another object is to provide such an analyzer that willeffectively analyze the vibrations caused by parts operating at verynearly the same speed.

These and other objects and advantages will be apparent to those skilledin the art from the following description and drawings which illustrateone form the invention may take and in which:

FIGURE 1 is a block diagram illustration of a complete vibrationanalyzer;

FIGURE 2 is a circuit diagram of a portion of the electrical andelectronic parts of the analyzer of FIG- URE 1',

FIGURE 3 shows a further portion of the circuit diagram;

FIGURE 4 shows still another portion of the circuit diagram;

FIGURE 5 shows another portion of the circuit diagram;

FIGURE 6 shows how the FIGURES 2 to 5 inclusive may be arranged to forma complete circuit diagram of the apparatus;

FIGURE 7 illustrates how a particular frequency is separated from twoother frequencies by the synchronous rectifiers; and

FIGURE 8 illustrates how the synchronous rectifiers provide an outputsignal to control the oscillator to maintain a correct phaserelationship.

Briefly the invention includes an amplifier that amplifies a complexelectrical signal produced by a vibration pickup connected to themechanism to be analyzed, such as an internal combustion engine. Theamplified vibration signal is then filtered by a pair of bridge typesynchronous rectifers. A sync signal or pulse is derived form therotation of one part of the apparatus being measured, such as one pulseper revolution of the crankshaft on the engine. This sync pulse is usedto form a rectangular wave signal having a fixed pulse duration andhaving the same frequency as the sync pulse. The rectangular wave signalis rectified and filtered to provide a main DC signal having anamplitude proportional to the frequency of the sync or reference pulse.A variable and determinable portion of this DC is used to control thefrequency output of a first square wave generator whose output isamplified and then used to control one of the synchronous rectifiers. Aportion of the output from this synchronous rectifier is fed back to theDC control of the oscillator and varies the phase of oscillator squarewave output until the rectifier output is zero. This occurs when thefirst square wave is 90 degrees out of phase with the component of thevibration signal having the same frequency as the sync signal. Theapparatus is calibrated so that the frequency of the square wave bearsthe same ratio to the sync frequency as the speed of the part producingthe vibration component does to the speed of the part providing the syncpulse.

The output of the square wave generator is also used to form a secondsquare wave having the same frequency as the first but 90 degrees out ofphase with the same. This 90 degrees phase shifted square wave is usedto control the second synchronous rectifier connected to the amplifiedcomplex vibration signal. The average DC value of the output of thesecond rectifier is indicated on an amplitude meter which can be used'toindicate absolute or relative magnitude of the vibrations of the engineoccurring at the frequency of the square wave. A second meter is used toselectively indicate either the frequency of the 90 degrees phaseshifted square wave which represents the frequency of the vibrationwhose amplitude is indicated on the amplitude meter, or alternatively,the frequency of the rectangular wave which represents the frequency ofthe sync pulse or speed of rotation of the reference or sync member suchas the crankshaft.

By switching between the plurality of fixed and calibrated voltagedividers, the percentage or portion of the main DC signal that is fed tothe DC controlled oscillator can be varied to change the ratio of themeasured vibration frequency to the reference frequency. For example ifa certain main DC voltage drive of the controlled oscillator produces anoutput having the same frequency as the sync frequency, then if 90percent of this certain DC voltage is fed to the oscillator, thefrequency of the measured vibration would be 90% of the referencefrequency. In the case of a cooling fan rotating at 90% of the speed orr.p.m. of the engine crankshaft, and where no other part or accessoryoperates at this 90% speed, then only the vibrations produced by the fanwill be indicated on the amplitude meter -when a 90% ratio drive of theoscillator is established. Also by providing a continuously variable anddeterminable voltage divider control of the percentage of the main DCfed to the oscillator, the complex vibration signal can be fully.analyzed by scanning through all speed ratios from a small fraction ofthe engine speed to a multiple of that speed.

Referring now to FIGURE 1 which shows a complete vibration analyzer inblock diagram form, it will be seen that theer is provided a vibrationpickup 1 which depending on the form thereof is connected to or placedin proximity with a stationary part of the mechanism whose vibrationsare to be analyzed. This pickup may be any type of transducer such asdisplacement, velocity, accelcrometer, microphone, etc., however, in thespecific example shown a velocity type pickup would be used. The pickup1 produces a complex electrical signal as shown having varioussinusoidal components. The pickup 1 is connected through a lead 2 to anattenuating resistance network 3 having a plurality of output taps towhich a displacement lever switch S1 can be selectively connected. Thecomplex vibration signal then passes through contacts on the deck a of athree deck four position switch S to a voltage amplifier 9. The switch Salso has decks b and c. The output of the voltage amplifier 9 isconnected through an integrator circuit 11 which changes thecharacteristics of the velocity responsive vibration signal to thatrepresenting displacement. The signal is then fed to a four stagevoltage and power amplifier 13. The output of amplifier 13 is fed intothe input primary of a transformer 15 which has its output secondaryconnected in parallel to a pair of bridge demodulators 17 and 19.

A sync signal or reference pulse, obtained from any suitable sourceproviding a signal or pulse having a frequency equal to the rotationalfrequency of the main mechanism, is applied at an input 21 at deck b ofthe switch S. This reference or sync signal may be obtained from anysuitable source such as the engine ignition, photo-electrical pickup,magnetic pickup, etc. The reference signal is fed through. an amplifier25 and then to a clipping and shaping network 26 which provides a oneper revolution sharp positive pulse for each revolution of themechanism. This sharp pulse is fed into and acts to control a one shotmultivibrator 27 that generates a rectangular wave having a frequencyequal to the frequency of the sync pulse and having a fixed pulseduration. This rectangular wave from the output of the one shotmultivibrator 27 is then fed into a buffer amplifier and clampingcircuit 29 which provides a negative DC output signal having a valuethat varies proportionally with changes in the frequency of therectangular wave pulses. The DC output of the circuit 29 is connected tosix position switch 31a-31h. Movable contacts 31a connects the DC to oneend of a plurality of potentiometers 33a-33f, inclusive.

The other ends of the potentiometers 33 are connected to ground. Theswitch 31a-31b has a second movable contact 31b, movable in unison withthe contact 31a, that connects the adjustable tap output of the selectedpotentiometer 33 to a ripple cancelling circuit 35. The potentiometers33a through 33j thus act a voltage dividers to supply a portion orpercentage of the DC output from the circuit 29 to the movable contact31b and circuit 3S. The signal from the ripple cancelling circuit 35 isconnected to a filter circuit 36 whose output is a pure DC voltage.

This DC voltage which is still ranged between 0 and a maximum negativevalue, is fed into a fixed ratio DC amplifier 37 the output of which isconnected to an internal oscillator 39 which may be a frequencycontrolled free running multivibrator. The oscillator 39 provides a pairof phase inverted square wave signals having a frequency proportional tothe input DC signal. The square waves produced by the oscillator drive apush-pull amplifier 41 whose output is connected to a transformer 43having a secondary connected across the bridge demodulator 19. A centertap 45 of the secondary winding of the transformer 43 is connected to avoltage divider potentiometer 47 whose movable center tap 48 isconnected through lead 49 to feed back a portion of the bridge output,if any, to the filter circuit 36 wherein it is combined with the outputfrom DC potentiometer 33.

The output from the push-pull amplifier 41 is also connected by a lead51 to a 90 degree phase shifter network 53 whose output is connected toa three stage squaring amplifier 55. The output from 55 in turn isconnected to a phase inverter 57. The output of the phase inverter 57 isa square wave having the same frequency as the square wave output of theamplifier 41 but displaced 90 degrees in phase therefrom. This 90degrees displaced square wave is amplified by a push-pull amplifier 59,the output of which is connected to the primary of an output transformer61. The secondary winding of the transformer 61 is connected across thebridge demodulator 17. A center tap 63 on the secondary of 61 isconnected through a low pass filter 65 to an amplitude meter 67.

The degrees phase shifted square wave output from the amplitier 59 canalso be connected through a switch S6 to a differentiating full waverectifying and filter circuit 71 eeding an r.p.m. or frequency meter 73.The switch S-6 can also be positioned to connect the rectangular waveoutput of the one shot multivibrator 27 to the full wave rectifier andfilter circuit 71.

FIGURES 2, 3, 4 and 5 together show the complete schematic circuit ofthe apparatus shown in block diagram form in FIGURE 1. FIGURE 6illustrates the relationship of FIGURES 2, 3, 4 and 5 to each other toform a complete circuit. Dashed boxes in FIGURES 2 to 5 are used toindicate the blocks in FIGURE 1 and corresponding reference numbers areused to indicate the complete groups of components making up the blocksof FIGURE l.

As seen in FIGURE 2 the signal from the vibration pickup is connected toan input lead 2. The voltage dividing or displacement level resistorgenerally indicated 3 consists of a series of resistors R1 to R7connected between the input 2 and the apparatus electrical ground. R1 isa variable resistor that is used to calibrate the input to provide fullscale meter detiection for various vibration displacements. Switch S1connects the various taps between the resistors R2 to R1 to contacts Sagand Sag of a three deck, four position switch S. The movable contact Sais connected directly to a preamplifier 9, specifically to the controlgrid of a triode amplifier tube V1.

It should be noted that in the circuit diagram of FIG- URES 2 to 5 thetube filaments and their supply voltages are not shown nor is the DC Bplus supply. The plate output from V1 is connected to an integratorcircuit 11 consisting of a resistor Rg and capacitor C1. This inte-vgrator network, as indicated previously in the description of FIGURE 1,changes the velocity responsive vibration Lifi signal from pickup 1 to adisplacement responsive signal. If an acceleration responsive pickupwere used, a second integrator network would be provided to change theacceleration signal to a velocity signal which would be changed to adisplacement signal by the network 11. The output from the integratornetwork 11 at the junction be tween R8 and C1 is fed into a four stagevoltage and power amplifier generally indicated 13 and consisting ofcapacity coupled amplifier triodes V2, V3, V4 and V5.

Resistors Rg and R10 provide a voltage divider to place a portion of theoutput of V5 across a neon tube Ne1 which functions as an amplifier overdriven signal light. During use of the apparatus the input displacementselector switch S1 is adjusted to the position wherein Ne1 does notlight which indicates distortionless operation of amplitier 13. Outputleads 14 and 16 connect the signal output from the final amplifier tubeV5 developed between the plate thereof and cathode resistor R11 to theprimary winding of transformer 15, FIGURE 5. The secondary winding oftransformer 15 has a grounded center tap while the ends thereof areconnected to opposite junction terminals 17a and 17c'of a diode bridgecircuit 17 andv terminals 19a and 19C of bridge 19 as seen in FIGURE 5.

The bridge circuit 17 comprises series connected diodes D1, D2, D3 andD1 with current limiting resistors R12, R13, R14 and R15 in series withthe diodes. The second bridge circuit 19 is identical with bridge 17 andcomprises diodes D5, D5, D7 and D8 as well as resistors R16, R17,

R111 and R19, The bridges 17 and 19, in combination withtransformers 43and 61 respectively, each comprises a synchronous controlled demodulatoror rectifier circuit. The synchronizing or controlling signals for thebridges are applied at the pairs of opposite junctions 17b-17d and19h-19d.

Referring now to FIGURE 3, it will be seen that there is provided twosync or reference inputs to the analyzer. The first input includes leads20 and 22 that are suitable for connection to a photocell pickuprequiring a high voltage such as present on lead 20, for operation. Thereference pulse as supplied by the photocell appearing in lead 22 iscoupled to contact Sbz of switch S by a capacitor C2. The second syncinput comprising leads 23 and 23' are for use with pickups providingself generated pulses such as those obtained from magnetic, spark orignition sync pickups. A reversing switch S3 connects either input lead23 or 23' to the contact Sbg and the other of the input leads to theanalyzer electrical ground.

With the movable contact Sb in the position shown any sync signalapplied to either sync input will be coupled to the control grid oftriode V6. A circuit including resistors R20 and R21 and diode Dg andcontrolled by a switch S4 adjusts the input impedance of the synccircuit for high or low level sync pickups. V5 along with triode V7 forma two stage sync pulse amplifier 2S. The cut olf level of amplifier 25can be varied by adjusting the cathode potentiometer R22.

The amplified sync pulse from amplifier 25 is coupled through capacitorC3 to a clipping and shaping network 26. A neon tube Nez, capacitor C1and voltage dropping resistor R23 serve to establish a regulated voltageat the junction between R13 and a diode D10. Diode D11, and a seconddiode D11 allow only positive trigger sync pulses to pass to the grid ofa triode V11. VB and a second triode V9 together form a one shotmultivibrator network 27. C5, and R21 form a time constant control ofthe positive output pulse emitted by V9 after a positive pulse at thegrid of V8 causes the same to conduct. The one shot multivibrator 27therefore produces an on-ofi rectangular wave having a fixed durationpositive pulse occurring at the same frequency as the triggering inputpulse from the clipping network 26. The fixed time duration `pulseproduced at the plate of V9 is available at point A- for frequencymeasurement by a meter as shown in FIGURE 5, such measurement beingdescribed later.

The voltage on the plate of V3 of multivibrator 27 changes with that onthe plate of V2. As seen in FIG- URE 2 the plate of V2 is capacitycoupled to the grid of a triode V12 arranged in a reduced grid biascathode follower amplifier circuit 29. A negative clamping diode D12limits the cathode resistor output of 29 to a negative value. Thisoutput is connected through a calibration potentiometer R25 to onemovable contact 31a of a two deck six position switch 31a-31h. TheContact 31a in its various positions feeds the now all negativerectangular wave from the amplifier 29 to any of a series of resistors32b to 32f which are in series with adjustable resistors 33b to 33frespectively. Switch 31a-31!) also can be positioned to feed thereference or sync wave to potentiometer 33a. The adjustable taps ofpotentiometers 33a to 33j are arranged on the second deck oi' switch31a-31h where movable contact 3111` will connect the same to point B.The potentiometer 33a which may be a ten turn calibrated dial typepotentiometer which directly divides the voltage output from 29depending on the setting of the dial. Likewise the potentiometcrs 33b to33jf and series connected resistors 32h to 32f provide for adjustable,but normally fixed, voltage division of that output.

The clamped wave form at point B is filtered by an RC filter 36,including capacitors C and C5 and resistor R21. A switch S5 can beactuated to insert additional filtering by C7 and is used where thereare two vibrations having almost the same frequency.

The clamped signal at point B is fed back into a ripple cancellingcircuit 35 including V11 which inverts any ripple. The inverted rippleis fed back into the main sync circuit at point C where it acts tocancel original ripple.

The filtered and divided signal which is now a relatively pure negativeDC voltage at point D, is directly coupled into a DC amplier 37 circuitincluding triode V12, as seen in FIGURE 4. The output level of V12 canbe adjusted by a variable cathode resistor R23. The amplified and nowpositive DC from the plate of V12 is connected to a free runningmultivibrator oscillator 39 including triodes V13 and V11. The frequencyof the square wave output of the multivibrator, as it appears on theplates of V13 and V1.1. is varied by the DC output from V12 which actsto change the grid bias on the multivibrator tubes V13 and V1.1. Thecathodes of V13 and V1.1 are normally positively `biased by a voltagedivider including resistors R22, R35 and R31. The variable DC from DCamplifier V12 changes the bias on the grids of V13 and V1.1 and hencethe rate at which the cross coupling capacitors C22 and C23 charge. Thisin turn changes the frequency at which the multivibrator runs and hencethe frequency of the square wave outputs at the plates of V13 and V1.1.

The frequency controlled square wave outputs from the plates of tubesV13 and V1.1 are capacity coupled into a cathode follower push-pullamplifier 41 including triodes V15 and V15. Since the square wave fromV13 is displaced 18() degrees from the form V1.1, no inverter circuit 1snecessary to drive the push-pull amplifier 41. The tubes V15 and V15have their cathodes connected via leads 75 and 77 to opposite ends ofthe primary winding of a transformer 43, FIGURE 5. This primary has itscenter tap 76 directly connected to ground as shown in FIGURE 5. Thesecondary winding of transformer 43 is connected across junction points17b and 17d of the rectifier bridge 17. The center tap of this secondaryis connected by lead 79 to one end of the phase lock potentiometer 47.

The square Wave output at the cathode of V15, FIGURE 4, is alsoconnected by lead 51 through a coupling capacitor C3 to a two stepintegrator network 53 comprising a first integrator including resistorR32 and capacitor C3 and a second integrator including register R33 andcapacitor C in series with resistor R34. R32 and C3 are proportioned toprovide a substantial phase shift even at low frequencies while R33,R511 and C15 provide a small but fairly constant phase shift. The totalnetwork transforms the square wave from C5 to a 90 degree phase shiftedtriangular wave that is fed to the grid of a linear amplifier includingtube V11. The amplified triangular wave output from V13 is capacitycoupled through C11 to the grid of triode V13 through a grid limiterresistor R35. V13 is the first of two overdriven amplifiers fortransforming the triangular wave toa square wave by conventional gridand cutoff limiting action. A resistor R31, having the same value as thegrid limiter resistor R35, is in series with a diode D13 to provide adischarge impedance from C11, during negative operation of the grid ofV13, equal to the charging impedance of C11 during positive or gridcurrent operation. This makes the output or load impedance on V11 remainconstant during a full cycle and enables the squared wave produced atthe plate of V12 to have equal positive and negative swings.

The partially squared wave from V17 is coupled through C12 to a secondoverdriven amplifier. Grid resistor R39 discharge resistor R41 and diodeD11 perform the same function as R35, R33 and D13 respectively. Thesquare wave output at the plate of V12 is fed to the grid of V23 forminga single tube paraphase amplifier 57. The phase inverter outputs fromthe plate and cathode of V21, are coupled through C13 and C14 to thegrids of tubes V21 and V22 which form a push-pull cathode followeramplifier 59 identical with amplifier 41. The push-pull output from V21and V22 is applied through leads 81 and 83 to a center tappedtransformer 61, FIGURE 5, similar to transformer 43. The center tap ofthe primary of transformer 61 is grounded as shown.

The secondary winding of transformer 61 is connected through leads andS7 to the opposite junction points 19d and 19h of the rectifier bridge19. The center tap of the secondary winding of transformer 61 isconnected by a lead 89 to a low pass filter circuit 65 including C11,C15 and R42. The output from filter 65 is connected to one side of a DCamplitude meter 67 the other side of which is grounded as shown.

One end of the primary winding of transformer 61 is connected throughlead 91 to a pair of capacitors C12 and C19, the opposite ends of whichare connected to two stationary contacts of a three position double poleswitch S5. The third stationary contact is connected through a capacitorC211 to point A of FIGURE 3. The movable contact of Switch S5 isconnected to junction point 93a of a four diode full wave rectifierbridge including diodes D15. D15, D17 and D13. The opposite junction ofthe bridge is grounded as shown. A DC meter 73 is connected betweenjunction point 93b and junction point 93d through resistor R51 andeither variable resistor R53 or R55 depending on the position of switchS5. Resistor R52 and capacitor C21 provide damping for the meter 73. Theinput capacitors C12, C15 and C25 in combination with the resistancesR51, R53 and R55 and the internal meter resistance act to differentiateeither the square wave signal in lead 91 from the transformer 61 or therectangular wave from the one shot multivibrator 27, FIGURE 3, appearingat point A. The rectifier bridge comprising the diodes D15 to D15rectifies the differentiated signal and the DC meter 73 will indicatethe frequency of the signal from transformer 61 or multivibrator 27.

Variable resistors R53 and R55 provide for adjusting the input to meter73 to give a proper reading when a signal having a known frequency isfed to the same. The capacitors C13 and C12 provide two ranges of fullscale meter reading. Thus if C13 is one-half the value, i.e., .0l m.f.,of C13, i.e., .02 mf., then the full scale reading of frequency meter 73with switch S11 connecting the meter circuit to C13, will be twice thatas when connected to C13. When the analyzer is used to analyzevibrations of rotating parts, the meter 73 will read r.p.m. as well asfrcquency.

Operation While the subject analyzer could he used to analyze thevarious frequency components of any complex signal, the operation of theanalyzer will be explained by describing its use in analyzing thevarious speed related vibrations of an internal combustion engine andits accessories. Referring again to the block diagram of FIG- URE 1, thevibration pickup 1 would be connected at some suitable point of theengine. If the amplitude meter 67 were to be used to indicate actualdisplacement, a known unbalance producing a known vibration displacementwould be used to calibrate the analyzer. If it is merely desirable todetermine what engine component is producing an undesirable vibrationand what is its relative amplitude with respect to other vibrations,then the pickup 1 could be positioned at any point subject to thevibrations. When the engine is in a vehicle the pickup could be placedon the chassis, the body, but preferably on the engine itself.

A sync or reference pickup, not shown, would be connected to sync inputcontact 21. This pickup could either be an ignition pickup connected totwo ignition wires leading to spark plugs firing 360 engine degreesapart or to a magnetic or photocell pickup producing a pulse each enginerevolution, or any other means providing one pulse per enginerevolution.

The complex vibration signal from pickup 1 is attenuated by adjustmentof switch S1. With switch Sa in the Y position shown in FIGURE l, thesignal will be fed to the amplifier 9 where it is ampli-fied and fed tothe integrator 11. The integrator 11 changes the complex signal`produced by a velocity type pickup to that produced by a displacementtype pickup. In other words, the amplitude of the signal after it leavesintegrator 11 will be proportional to the amplitude of displacement ofthe pickup 1. This complex signal is further amplified and is applied toboth synchronous rectifier bridge demodulator 17 and 19 throughtransformer 15.

The reference or sync pulse at 21 is connected by switch Sb to the pulseshaping amplifier 2S which produces one sharp positive pulse each enginerevolution. This pulse is connected to trigger the one shotmultivibrator 27 which provides a constant width rectangular wave havingthe same frequency' as the reference input at 21. The buffer amplifierand clamping circuit 29 changes the reference level for this rectangularsignal so as to provide a negative DC signal whose value is proportionalto the frequency of the rectangular waveform and hence signal at 21. Apercentage or portion of this DC signal as determined by the setting ofswitch 31a-31h and the variable resistords 33a to 33jc is fed to theripple cancelling circuit 35 and filter circuit 36 and then to the DCamplifier 37. The DC amplifier 37 provides a positive DC signal whosevalue is both proportional to the engine r.p.m. and to the speed ratioof the engine to that part whose vibration is being measured. This valuemay be visually indicated at each setting of the switch 31a-31h.

The DC output from amplifier 37 is fed to the frequency controlledoscillator 39 which produces a square wave whose frequency is linearlyproportional to the value of the DC input to the osciilator. This squarewave signal is amplified by the push-pull amplifier 41 and fed to theprimary of transformer 43. The secondary of 43 is connected across thebridge 19 to cause synchronous rectification of the complex vibrationsignal fcd to the bridge 19. The center tap 45 of the transformer 43will then have an output determined by the phase relationship betweenthe square wave output from oscillator 39 and the component of thecomplex vibration signal whost frequency is equal to that of the squarewave.

FIGURE 7 illustrates how the synchronous rectifier bridges 17 and 19operate to separate a selected frequency F from two other frequenciesl.5F and .75F. The square wave 95 at a represents the switching actionof the `synchronous rectifier. When the square wave is phased as shownwith the selected frequency component 97 of the complex signal therectified output appears as the wave 99 in b which has an averagepositive DC value 101. Frelll quency 1.5F is scrambled by the rectifieraction in such a manner as seen in c that its average DC value is zero.Areas above and below the center line exactly cancel each other.Similarly, frequency .'75F is also rectified to produce an average DCoutput of zero. Essentially all frequencies other than F and oddharmonics of F are cancelled out by the synchronous rectifier action.

FIGURE 8 illustrates how the feed back from bridge 19 acts to controlthe phase ofthe rectifying square wave produced by the oscillator 39until the square wave and selected frequency component are 90 degreesout of phase. If the output from bridge 19, at the center tap 45, is asshown at b, a positive DC signal is fed to the oscillator which'momentarily slightly raises the frequency output until the square wavecontrolled rectification of the selected frequency component produces abridge output as shown in d. If the feed back from bridge 19 is like thewaveform of FIGURE 8U) a negative signal is fed back to be added to theinput to oscillator 39 to momentarily slightly decrease the frequencyoutput of the same until the FIG- URE 8U!) or zero average DC output isattained. When the square wave output 40 from oscillator 39 is locked in90 degrees out ofV phase with the selected frequency component, thesquare wave outputv58 from the phase shifting and squaring systemincluding 53, 55, 57 and 59, will act through demodulator bridge 17 torectify the selected frequency component to produce the wave form shownin FIGURE Stb). The average value of this positive DC voltage isproportional to the amplitude ofthe selected frequency only and is whatis shown on the amplitude meter 67.

The frequency of the selected frequency component is indicated by themeter 73 which measures the frequency ofthe rectifying square wave fromthe push-pull amplifier 59. The meter 73 is normally calibrated incycles per minute. This selected frequency bears a certain ratio to thefrequency output of the one shot multivibrator 27. This ratio isdetermined by the setting of whatever voltage dividing resistor 33a to33j is connected by switch 31 to the DC amplifier. The frequency outputof the one shot multivibrator 27 can be checked by switching therectangular wave output at point A to the frequency meter rectifier 71.This is accomplished by switch S5.

Since the frequency of the output of multivibrator 27 is equal to thesync input frequency at 21, the meter 73 will then also give thefrequency of the reference or sync signal, which in the case of anengine vibration application is equal to the rpm. of the engine. Thus ifthe engine is operating at 1800 r.p.m. the meter will read 1800 cyclesper minute or 30 cycles per second. The oscillator output frequency iscalibrated by selection of its frequency determining component as wellas the fixed amplification of the DC amplifier 37 to provide an outputhaving a one-to-one frequency ratio with respect to the sync signal whenone tenth of the value of the DC from circuit 29 is applied to the DCamplifier. Therefore if 33a is a ten turn potentiometer that iscalibrated from 0 to 10, and the ratio selector switch 31 connects theoutput of circuit 29 to the DC amplifier 37 through the potentiometer33a, the frequency of the square wave output of oscilla.4 tor 39 willbear the ratio to the frequency of the sync signal applied at 21numerically equal to the setting of the 0-10 potentiometer 33a. Thus ifthe sync signal is 1800 cycles per minute and the ratio dial ofpotentiometer 33a is set for 0.5, the output frequency of the oscillator39 will be 900 cycles per minute or l5 cps. Similarly if the ratio dialis set for 2.5 then the oscillator 39 will provide an output of 2.5X18OOor 4500 cycles per minute. As the frequency of the sync input to 21changes with engine speed changes, the frequency output of oscillator 39will change proportionally but will always bear the same ratio to thesync input unless the ratio dial 33a is changed.

The other positions of 311) will connect the DC output from circuit 2.9to the DC amplifier 37 through any of the other voltage dividers 33h to33j. These can be previously set to provide fixed ratios. For example,if the engine fan is driven at 0.9 times the engine speed, resistor 3317could be set to provide 0.09 of the DC output from 29 to the DCamplifier. Then when ever it is desired to determine the amplitude ofvibration of the engine fan, the switch 31a-31h can be switched toconnect 33b into the circuit and the oscillator 39 will adjust itsfrequency output supplied to the bridges 17 and 19 so that onlyvibrations occurring at a frequency 0.9 times engine speed will havetheir amplitude indicated on meter 67.

Likewise if the generator runs at 2.3 times engine speed, 33C could beset to provide 0.23 or 23% of the reference DC voltage to the amplifier37. Again with switch 31 connected to 33e only vibrations occurring at2.3 times engine speed would be indicated on meter 67. In the samemanner 33d could be set to the cam shaft frequency, 33e at the powersteering pump frequency, etc.

In the position shown, the sync selector switch S with its three decksSa, Sb and Sc will connect the vibration signal from the external pickupto amplifier 9 and the sync signal to the pulse shaping amplifier 25 asshown. Sc does not connect to anything in this position. In FIG- URE 3this position of switch S corresponds to the Use Ext position.

If switch S is moved to the Use Line position deck Sc will connect pulseshaping amplifier to a line or 60 cycle voltage source to cause the oneshot multivibrator to produce a 60 cps. or 3600 c.p.m, output. If S6 isthen set to feed the output of multivibrator 27, point A, to the meter73, then the meter should read 3600. With the sync selector switch inthe Use Line position the deck Sa still feeds the external vibrationsignal to the voltage amplifier 9. This allows use of the analyzer whenno external sync signal is available. The filtering frequency is set asa ratio to line frequency (3600 cpm.) by the ratio dial 33a.

If the sync selector switch S is moved to its Cal RPM position Sc feedsa 60 cycle signal to the pulse shaping amplifier 25 to drive or triggerone shot multivibrator 27 to provide a rectangular 60 cps. output forcontrolling the internal oscillator 39. Deck Sa simultaneously connectsthe voltage amplifier 9 to -this 60 c.p.s. output via a lead 103. Whenthe oscillator 39 locks on this signal, with the ratio dial 33a switchedin and set for l, the r.p.m. meter should read 3600 both when SG is setfor reading the frequency output of multivibrator 27 or when set forreading the square output of amplifier 59 (internal oscillatorfrequency). R53 in the frequency meter circuit shown in FIGURE 5 can beadjusted to make the meter 73 read 3600 if it does not with S in Cal RPMposition.

The fourth position of the sync selector switch S is the Ext-Cal Dialposition as seen in FIGURE 3. With S in this position the output fromthe neon tube oscillator circuit 24 is fed to the vibration signalamplier 25. This neon oscillator would normally be designed to provide arelatively low frequency output for example 8 to 10 c.p,s. equivalent to480 to 600 r.p.m. The output from the one shot multivibrator 27 isconnected by deck Sa to the vibration voltage amplifier 9. When theratio dial 33a is set for one-to-one ratio, the oscillator should lockon this signal.

The amount of signal from the bridge 19 that is fed back to control thephase of oscillator 39 can be varied by the potentiometer 47. With toolittle feed back, the pointer on the amplitude meter 67 will oscillateat a frequency equal to the difference between the oscillator andcomponent frequencies. With too much feed back the oscillator may notlock in on the smaller of two Components close together in frequency.Thus 47 would be adjusted to feed just enough signal back to cause theoscillator to lock in with the component being measured.

The amplifier ovcrdriven neon light Nel will indicate that the vibrationsignal from pickup l is too large. In such a case the switch Sx can beturned to feed a smaller part of the vibration signal to the voltageamplifier 9 and hence give a larger full scale reading on the amplitudemeter 67.

It will be seen from the above that we have provided a method andapparatus for analyzing complex waveforms and determining the amplitudeand frequency of sinusoidal components of the signal that are very closeto gether. A minimum amount of experience is needed for operating theapparatus since there is no extended calibration necessary each time theapparatus is used.

By merely positioning a vibration pickup and making two connections tothe engine ignition system only simple switching from one presetfrequency ratio to another will provide a complete analysis ofcomponen-t vibrations in an engine assembly. This whole procedure can beaccomplished in a matter of a few minutes. After determining that acomponent is causing excessive vibration, it can either be corrected orreplaced.

Other uses as well as modifications will be apparent to those skilled inthe art. Such uses and modifications and other changes are deemed to bewithin the scope of the invention which is limited only by the followingclaims:

What is claimed is:

1. Vibration analyzer apparatus comprising vibration pickup means fordeveloping a complex electrical vibration signal having combinedfrequency components each bearing a fixed frequency ratio to the speedof a rotating member, means for producing an electrical pulse for eachrevolution of the rotating member, frequency responsive means connectedto the pulse producing means for deriving a variable electrical signalvarying with changes in the repetition frequency of the electricalpulses, signal ratio control means having the variable electrical signalapplied thereto to produce a variable and determinable portion of thevariable electrical signal wherein the signal portion is proportional tothe fixed frequency ratio of one of the frequency components of thecomplex electrical vibration signal, variable frequency oscillator meansconnected to the signal ratio control means and responsive to the signalportion for producing an oscillator output signal having a frequencyequal to the one vibrational frequency component, a pair of synchronousrectifier circuits operatively connected to the vibration pickup means,amplifier means connected to the output of the oscillator and applying afirst synchronous control signal to one of the synchronous rectifiercircuits to control the rectification of the complex signal beingapplied thereto from the pickup means, circuit means providing a portionof the output of the one synchronous rectifier circuit to the variableoscillator input to vary the phase of the oscillator output signalrelative to the phase of the one vibrational frequency component so thata predetermined phase relationship is maintained therebetween when theone synchronous rectifier has a zero average DC output signal, a controlsignal source supplying the output of the oscillator to the other of thesynchronous rectifiers to provide a second synchronous control signalhaving the same frequency as the signal output of the oscillator and aphase displaced 90 degrees from the oscillator output signal, andmeasuring means connected to the output of the other synchronousrectifier and responsive to the second synchronous control signal forindicatig the amplitude of the one vibrational frequency component.

2. Vibration analyzer apparatus including vibration pickup means fordeveloping a complex electrical vibration signal having combinedfrequency components each bearing fixed ratios to the speed of arotating member, means responsive to the rotation of the member toprovide a variable DC signal varying with changes in the rotationalspeed of the member` a pair of phase sensitive synchronous rectifiercircuits operatively connected to the vibration pickup means, a signalratio Control means having applied thereto the variable DC signal andproducing a variable and determinable portion of the variable 13 DCsignal wherein the signal portion is proportional to the fixed frequencyratio of one of the frequency components of the complex vibrationsignal, oscillating circuit means having a variable frequency output andan input connected to the signal ratio control means to provide anoscillating circuit means output signal having a frequency equal to theone vibrational frequency component, circuit means connecting the outputof the oscillating means to one of the synchronous rectifiers to controlthe rectification of the complex electrical signal being applied theretofrom the pickup means, the one synchronous rectifier circuit providing arectifier output signal connected to the input of the oscillatingcircuit means to vary the phase of `the oscillating circuit outputrelative to the phase of the one vibrational frequency component so thata predetermined phase relationship is maintained therebetween when theone synchronous rectifier has a zero average DC output signal, phaseshifting and waveforming circuit means connecting the output of theoscillating circuit means to the other of the synchronous rectifiercircuits to provide a synchronous control signal having the samefrequency as the output ofthe oscillating means and phase displaced 90degrees from the oscillating circuit output, and measuring meansconnected to the output of the other synchronous rectifier andresponsive to the synchronous control signal for indicating the averageDC quantity of the rectified waveform output produced by the othersynchronous rectifier wherein the average DC quantity corresponds to theamplitude of the one vibrational frequency component.

3. Vibration analyzer apparatus comprising a vibration pickup means fordeveloping a complex electrical vibration signal having combinedfrequency components each bearing a fixed frequency ratio to the speedof an assembly having a plurality of members each rotating at a speedhaving a predetermined ratio relative to the speed of a main rotatingmember, means for producing an electrical reference pulse for eachrevolution of the main member, circuit means connected to the referencepulse producing means to provide a variable DC signal varying withchanges in frequency of the electrical reference pulses, a pair of phasesensitive synchronous rectifiers operatively connected to the vibrationpickup means, a variable frequency oscillator, a signal ratio controlmeans connected between the circuit means providing a variable DC signaland the variable frequency oscillator to alter the variable DC signaland produce a variable and determinable portion of the DC signal to theoscillator to cause the frequency of the oscillator output signal toequal the frequency of one of the vibrational frequency components,circuit connecting means applying the output signal of the oscillator toone of the synchronous rectifiers to control the rectification of thecomplex electrical vibrational signal being applied thereto, the onesynchronous rectifier circuit providing a rectifier output signalconnected to the variable frequency oscillator input through a circuitmeans to vary the phase of the oscillator output signal relative to thephase of the one vibrational frequency component so that a predeterminedphase relationship is maintained therebetween when the one synchronousrectifier has a zero average DC output signal waveform, phase shiftingand waveforming circuit means connecting the output of the oscillator tothe other of the synchronous rectiers to provide a synchronous controlsignal thereto having the same frequency as the output signal of theoscillator circuit and phase displaced 90 degrees from the oscillatorsignal output, measuring means connected to the output of the othersynchronous rectifier and responsive to the synchronous control signalfor indicating the average DC quantity of the rectified waveform outputproduced by the other synchronous rectifier wherein the average DCquantity corresponds to the amplitude of the one vibrational component.

4. The apparatus of claim 3 wherein the signal ratio control meansincludes a variable voltage divider means 14 having an indicating meansoperably connected to the voltage divider means to directly indicate theportion of the variable DC signal supplied to the oscillator.

5. The apparatus of claim 3 wherein the signal ratio control meansincludes a plurality of selectable voltage divider circuits providingselective portions of the variable DC signal supplied to the oscillator,the voltage divider circuits providing a predetermined signal ratioproportional to the ratio of the rotational speed of each of theplurality of members to the speed of the main member, and a switch forselectively and operatively connecting the voltage divider circuits intothe circuit of the signal ratio control means.

6. The apparatus of claim 3 wherein a frequency measuring and indicatingmeans are provided and a selective connecting means which connects theelectrical reference pulse or a signal having the same frequency as theoscillator output signal to the frequency means thereby providing meansfor measuring the frequency of the oscillator output or the electricalreference pulse. l

7. Vibration analyzer apparatus including vibration pickup means fordeveloping a complex electrical vibration signal having combinedfrequency components each bearing fixed ratios to the speed of arotating member,fmeans for producing an electrical reference pulse foreach revolution of the rotating member, one-shot multivibrator meansconnected to the reference pulse producing means and responsive to theelectrical reference pulses to produce a rectangular wave output pulsehaving a fixed pulse width,

rectifier means connected to the rectangular wave pulse output toprovide a variable DC signal varying with changes in the frequency ofthe electrical reference pulses, a pair of phase sensitive synchronousrectifiers, transformer means operatively connecting the vibration`pickup means to each of the synchronous rectifiers, a free run ningmultivibrator oscillator, signal ratio control means connected to therectifier means to alter the variable DC signal and produce a variableand determinable portion of the variable DC signal, the signal portionbeing supplied to the free running multivibrator to cause the frequencyof the multivibrator oscillator outputsignal to correspond to thefrequency of one of the frequency components of the complex vibrationalsignal, transformer means connecting the output of the free runningmultivibrator oscillator to one of the synchronous rectiers therebyproviding a signal to control the rectification of the electricalvibration signal being applied thereto, circuit means connecting therectified output of the one synchronous output rectifier to the input ofthe free running multivibrator oscillator to vary the phase of theoscillator output signal relative to the phase of the one frequencylcomponent of the complex electrical vibration signal so that apredetermined phase relationship is maintained therebetween when the onesynchronous rectifier has a zero average DC output signal, phaseshifting and waveforming circuit means connecting the output of the freerunning multivibrator oscillator to the other of the synchronousrectifiers to provide a synchronous control signal in the form of asquare wave having a frequency equal to the oscillator output frequencyand a phase displaced degrees therefrom, and measuring means connectedto the output of the other of the synchronous rectiers and beingresponsive to the synchronous control signal for indicating the averageDC quantity of the waveform output produced by said other of thesynchronous rectitiers wherein the average DC quantity corresponds tothe amplitude of the one vibrational frequency component.

8. Waveform analyzer apparatus for analyzing a complex electrical signalhaving combined frequency components each having a certain ratio to thefrequency of the system generating the complex electrical signalincluding; means generating a first square wave signal having afrequency proximate to the frequency of a selected component whoseamplitude is to be measured,

the first square wave generating means including means producing asynchronizing signal having a certain frequency relation to the speed ofthe system and control means operative to modify the synchronizingsignal so as to develop the square wave signal of the frequencycorresponding to that of the selected component, first phase sensitiverectifier means having the complex electrical signal applied thereto,circuit means connecting the square wave generating means to the firstphase sensitive rectifier means to provide thereto a signal to controlthe rectification of the complex signal, feedback means connecting theoutput of the first rectifier means to the square wave generating meansto vary the phase of the generating means output relative to the phaseof the complex signal frequency component being measured whereby thefirst rectifier means is controlled to maintain a zero average DC outputsignal and the square wave generating means will lock-in on thefrequency of the selected component, means for generating a secondsquare wave signal having a phase displaced 90 degrees from the phase ofthe first square wave signal and having the same frequency as the firstsquare wave signal, second phase sensitive rectifier means responsive tothe complex electrical signal the second square wave signal also beingapplied to the second phase sensitive rectifier means to provide acontrol signal so that the complex signal is rectified in accordancewith the second square wave signal, and measuring means connected to theoutput of the second rectifier means to indicate the average of the DCsignal produced by the second rectifier means wherein the secondrectifier output signal corresponds to the amplitude of the frequencycomponent being measured.

9. The apparatus of claim 8 including frequency measuring and indicatingmeans to provide an indication of the frequency of the output signalfrom one of the square wave generating means.

`10. Waveform analyzer apparatus for analyzing a cornplex electricalsignal having combined frequency cornponents each having a certain ratioto the frequency of the system generating the complex electrical signalincluding means for generating a first square wave electrical signalhaving approximately the frequency of a selective component whoseamplitude is to be measured, the first square wave generating meansincluding means producinga a synchronizing signal having a certainfrequency relation to the speed of the system and control meansoperative to modify the synchronizing signal so as to develop the squarewave signal of the frequency corresponding to that of the selectedcomponent; phase sensitive rectifier means including a rectifier bridgecircuit having four diodes connected in a series loop and forming fourjunctions between each of the diodes, a first transformer meansincluding a first winding being connected to the complex electricalsignal and a second winding connected across two opposite junctions ofthe bridge circuit, a second transformer means including a first windingconnected to the first electrical square wave signal generating meansand a second winding connected across the other two opposite junctionsof the bridge circuit to connect the first electrical square wave signalgenerating means to the bridge circuit and to control rectification ofthe complex electrical signal, each of the second windings of the rstand second transformer means having center taps providing a rectifiedoutput signal to the square wave signal generating means to vary thephase of the generating means output relative to the phase of thecomplex signal frequency component being measured so that apredetermined phase relationship is maintained therebetween when therectifier signal output of the rectifier means has a zero average DCsignal and the square wave generating means will lock-in on thefrequency of the selected component so as to generate a square wavesignal of the same frequency as the selected component; means forgenerating a second square wave 90 degrees out of phase Cal with thefirst square wave signal and having the same frequency as the firstsquare wave signal, a second phase sensitive rectifier means including arectifier bridge circuit comprising four diodes connected in a seriesloop and forming four junctions between each of the diodes, the firsttransformer second winding being connected across two opposite junctionsof the second bridge to connect the complex electrical signal to thesecond bridge, third transformer means including a first windingconnected to the second square wave generating means and a secondwinding connected across the other two opposite junctions of the secondbridge, the third transformer second winding having a center tapproviding with the center tap of the first transformer the output of thesecond bridge, and means for measuring the average DC signal output ofthe second bridge and accordingly the amplitude of the one frequencycomponent of the complex electrical signal being measured.

11. A vibration analyzer for analyzing mechanical vibrations as afunction of the speed of rotation of a rotating member in a vibrationproducing apparatus comprising, means for converting the mechanicalvibrations into a complex electrical signal, electrical filter meanshaving the complex electrical signal applied thereto and beingresponsive to the complex electrical signal to separate a certainfrequency component therefrom wherein the frequency component is relatedto a mechanical vibration selected for analysis, the filter meansincluding a synchronous rectifier circuit means for synchronouslyrectifying the complex signal, means responsive to the speed of rotationto develop a control signal having a controllable frequency that varieswith changes in the speed of rotation of the rotating member, the speedresponsive means supplying the controllable frequency control signal tothe synchronous rectifier circuit, manually controllable signalproportioning means to proportionately vary the controllable frequencycontrol signal as a variable and determinable ratio of the speed of therotating member, phase and frequency control means providing a feedbacksignal to the speed responsive means from the filter means for varyingthe phase of the control signal and thereby establishing a certain phaserelationship between the rectified output produced by the synchronousrectifier circuit and the certain frequency component of the complexelectrical signal so as to coincide the frequency of the control signalwith the frequency of the certain frequency component, and measuringmeans to indicate the relative amplitude of the certain separatedfrequency component wherein the frequency of the component is equal tothe frequency of the control signal and the relative amplitude indicatedby the measuring means is maintained at a maximum by the phase controlmeans maintaining a predetermined phase relationship between the controlsignal and the certain separated frequency component, whereby theindicated amplitude of the frequency component is also an indication ofthe selected mechanical vibration being analyzed.

12. A vibration analyzer for analyzing mechanical vibrations as afunction of the speed of rotation of a rotating member in a vibrationproducing apparatus cornprising, means for converting the mechanicalvibrations into a complex electrical signal, electrical filter meanshaving the complex electrical signal applied thereto separate a certainfrequency component therefrom which is related to a mechanical vibrationselected for analysis, the filter means including a synchronousrectifier circuit means for synchronously rectifying said signal at acontrollable frequency supplied by a control signal, oscillator means toproduce a periodically varying control signal having an output frequencythat varies in response to changes in speed of the rotating member ofthe vibration producing apparatus, means connecting the oscillator tothe rectifier circuit means to apply the control signal thereto,manually controllable signal ratio control means controlling thefrequency of the control signal as a variable and determinable ratio ofthe speed of rotation of the rotating member, phase and frequencycontrol means providing a feedback signal to the oscillator means fromthe filter means for varying the phase of the periodically varyingcontrol signal relative to the phase of the certain separated frequencycomponent of the complex electrical signal thereby establishing acertain phase relationship between the rectified output produced by thesynchronous rectifying circuit and the certain frequency componentduring the rectification of the complex electrical signal by the filtermeans so as to lock in the oscillator means on the frequency of thecertain frequency component and coincide the frequency of theperiodically varying control signal therefrom with the frequency of thecertain frequency component, means for indicating the relative amplitudeof the certain separated frequency component when the frequency of thefrequency component is equal to the frequency of the control signal andthe indicated relative amplitude is maintained at a maximum indicationby the phase control means maintaining a predetermined phase between thecontrol signal and the certain separated frequency component whereby theindicated relative amplitude is an indication of the amplitude of theselected mechanical vibration being analyzed.

13. Apparatus for analyzing the vibration characteristics of selectedparts of a rotating system comprising vibration pickup means fordeveloping a complex electrical vibration signal having combinedfrequency components each representing the speed of one of the parts andeach having -a fixed frequency ratio to the speed of a rotating system,means producing a synchronizing signal having a certain frequencyrelation to the speed of the system, control means operative to modifythe synchronizing signal so as to develop a modified signal of afrequency corresponding to that of the frequency component of the partselected to have the vibrations thereof analyzed, the control meansbeing infinitely variable over a predetermined range so that anyfrequency component within the predetermined range can be analyzed,means mixing the complex signal and the modified signal so as to developa certain output when the component .corresponding to the rotationalvelocity of the selected part is isolated, feedback means supplying afeedback signal refiecting the output from the mixing means to thecontrol means so as to cause the modified signal to be altered until thefrequency of the modified signal coincides with the frequency of theselected frequency component, and means measuring the component so as topermit an analysis thereof.

:14. The apparatus described in claim 13 wherein the Control meansincludes a manually variable frequency altering network -for changingthe frequency of the synchronizing signal so as to develop a modifiedsignal of a frequency corresponding to that of the frequency componentof selected different ones of the parts and means developing a pair of9() degree phase displaced modified signals, wherein the mixing means isa pair of demodulators, one for each of the pair of modified signals,and wherein the measuring means is coupled to both of the demodulatorsand adapted to measure the frequency and also the amplitude of thefrequency component of the Selected part.

15, Apparatus for analyzing the vibration characteristics of selectedparts of a rotating system comprising vibration pickup means `fordeveloping a complex electrical vibration signal having combinedfrequency components each representing th'e speed of one of the partsand each having a fixed frequency ratio to the speed of a rotatingsystem, means producing a synchronizing signal havin-g a certain-frequency relation to the speed of the system, control means operativeto vary both the phase and the frequency o'f th'e synchronizing signaland develop therefrom a modified signal, means mixing the complex signaland the modified signal so as to develop a certain output when thecomponent corresponding to the rotational velocity of the selected partis isolated, feedback means supplying a feedback signal reflecting theoutput from the mixing means to the control means so as t0 cause themodified signal to be of a frequency coinciding with the frequencycomponent of the part selected to have the vibrations thereof analyzedand of a predetermined phase relationship with the frequency componentso as to cause the mixing means to develop the certain output, and meansmeasuring the component so as to permit an analysis thereof.

16. Apparatus for analyzing the vibration characteristics of selecte-dparts of a rotating system comprising vibration pickup means fordeveloping a complex electrical vibration signal having combined`frequency components each representing the speed of one of the partsand each having a fixed frequency ratio to the speed of a rotatingsystem, means producing a synchronizing signal having a certainfrequency relation to the speed of the system, control means operativeto modify the synchronizing signal, the control means includinggenerating means communicating with the synchronizing signal producingmeans and operative to develop a modified signal of a frequencydetermined by the input thereto, means mixing the complex signal and themodified signal so as to develop a certain output when the frequencycomponent corresponding to the rotational velocity of the part selectedto have the vibrations thereof analyzed is isolated, feedback meanssupplying a feedback signalA refiecting the output from the mixing meansto the input of the generating means so as to cause the modified signalto have a frequtncy coinciding with the frequency of the selectedfrequency component, and means measuring the component so as to permitan analysis thereof.

17. A method of analyzing the frequency components of a complexelectrical signal developed by different parts of vibration producingapparatus including Ithe steps of supplying said complex signal to asynchronous rectifier, providing a reference pulse having the samefrequency as one of the components of said signal, converting saidIpulse to a DC signal having a value dependent on the frequency of saidreference pulse, selecting a predetermined portion of said DC signal,said portion corresponding to the frequency component of a part whosevibrations are being analyzed, converting said DC portion to a squarewave having a frequency dependent on the value of said DC sign-al,synchronously rectifying said complex signal with said square wave inthe synchronous rectifier to filter out all frequency components exceptthat having the same frequency as said square wave, and measuring themaximum value of the frequency component passed through the rectifierand accordingly the amplitude of the vibrations of said part.

`18. Apparatus for analyzing the vibration characteristics of selectedparts of a rotating syste-m comprising vibration pickup means fordeveloping a complex electric vibration signal having combined frequencycomponents each representing the speed of one of the parts and eachhaving a fixed frequency ratio to the speed of the system, meansproducing a synchronizing signal having a certain frequency relation tothe speed 0f the system, control means operative to modify thesynchronizing signal, the control means including generating meanshaving the input thereof communicating with the synchronizing signalproducing means and operative to develop a modified signal of afrequency and of a phase determined by thex input thereto, means mixingthe `complex signal and the modified signal so as to develop an outputcorresponding both to the difference between the frequencies of themodified signal and a selected frequency component rep resentative of avibration characteristic of a'selected part and to variations from apredetermined phase relationship between the modified signal and thefrequency cornponent, and lfeedback means supplying a feedback signalrefiecting the output from the mixing means to the input of thegenerating means so as to cause the mixing means to develop a nulloutput when the modilied signal has a frequency coinciding with thefrequency of the selected frequency component and also the predeterminedphase relationship is established, and means measuring the selectedfrequency component s0 vas to permit an analysis thereof.

19. The apparatus as described in claim 21 including means producing arectifying signal 90 degrees phase displaced from the modied signal, andwherein the mixing is also operative to mix the rectifying signal andthe complex signal `and develop a full wave rectified output of anaverage DC level corresponding to that of the frequency component andaccordingly representing the amplitude of the vibrations of the selectedpart.

References Cited UNITED STATES PATENTS MacKenzie 73-71.4 X King 73--462Guanella B24-77 King 73-462 Burrow.

Lash et al 73-462 Sinchling 321-4 Joline 73-71.4 Losher 324-77 Cook324-77 D JAMES J, GILL, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,376,733 April 9, 1968 Philip K. Trimble It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 4 line 3l "theer" should read there 5 line 74 "contacts" vshouldread contact Column 5 line 6, "act a" lshould read act as -I- Column 6line 66 "C5 should read C5 Column 7 line 70 "register" shouldreadresistor Column 8 line 19, "function" should re d function line Z2"inverter" should read inverte "T e Column 9 line 14, "When" should readWhere line 48 "resistords" should read resistors Column l0 'line 52"component" should read components Column l5 lines 44 and 45"producinga" Should read producing Column 16 line 63 after "thereto"insert to Column l8 line 32 "frequtncy" should read-- frequency Column20 line 5 2 ,552 ,369" Should read 2 ,S22 ,369 line 9 "Sinchling" should'read -f Sichling Signed and sealed this 2nd day of September 1969(SEAL) Attest:

EDWARD M.PLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting OfficerCommissioner of Patents

